In the operation of many types of internal combustion engines which utilize fuel injection, it is necessary to accomplish optimum fuel-air mixing in order to achieve a more efficient engine operation. This mixing is normally done by the initial compression of the air charge within the compression chamber, after which a desired amount of fuel is introduced into said chamber. The fuel is normally forcibly injected in a concentrated or dispersed spray depending on the disposition of the chamber, as well as on other factors related to the combustion process.
One facility for achieving better combustion resides in the use of a cup-like cavity or depression formed within the face of the piston. This cavity, when of the correct shape and proportions, and when properly arranged with respect to the fuel injector, serves to both mix the fuel with compressed air, as well as to promote a more even combustion process. The latter will usually result in an overall more efficient engine operation.
One detriment inherent to the use of the so-called cup-in-piston arrangement, is that when a pressurized stream of fuel is injected into the cup-like cavity, the fuel will often strike a relatively cold part of the cup wall. This frequently results in condensation of at least a part of the fuel stream into minute particles, which further promotes the production of smoke leaving the engine exhaust system.
Further, since the fuel is in condensed or droplet form it will necessitate an extended residence time to be properly mixed and burned, thereby to avoid the presence of a smoky component in the exhaust stream.
Another factor which contributes to a smoky exhaust condition, is the inability of formed soot to burn within a combustion chamber. This further accentuates the desirability of avoiding the presence of fuel particles which result from the fuel impingement on the combustion chamber walls.
Toward overcoming this inherent problem of excessive exhaust smoke and heat loss in an engine of the type contemplated, there is presently provided means for insulating the shaped cavity in the piston head from the piston body. This is achieved through use of a cup-like insertable member which, when assembled, is substantially thermally separated from the remainder of the piston by a series of intermittently spaced apart support means. Such positioning tends to avoid excessive heat loss, and non-uniform cooling of the combustion chamber itself due to heat transfer through piston walls.
An object of the invention therefore is to provide a novel piston structure for an engine, which promotes a more rapid and uniform combustion of a fuel-air mixture. A further object is to provide a piston for an engine which utilizes fuel injection wherein the walls of the combustion chamber are so arranged to avoid the creation of smoke during the combustion process. A still further object is to provide a piston having a cavity formed in the head, being adaptable to promote a uniform combustion process while avoiding the occurrence of cold sections on the piston cavity wall which result from heat losses through the piston and into the engine cooling system.